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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 271 records · Page 15
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NASA NTRS1984

Ultraviolet high-resolution spectroscopy of the X-ray binary Sk 160/SMC X-1

High-resolution IUE spectra of Sk 160, the optical counterpart of the X-ray source SMC X-1, show substantial variations with orbital phase of the resonance P Cygni profiles. These variations are ascribed to the changing ionization state in the stellar wind caused by the X-rays emitted by the companion, as suggested by Hatchett and McCray and first established for the galactic X-ray binary Vela X-1. Furthermore, the profile observed during X-ray eclipse differs significantly from profiles of similar stars in the absence of X-ray ionization.

Hammerschlag-Hensberge, G.↗
NASA NTRS1993

Fabrication of micro-optical devices

We have fabricated a variety of micro-optic components including Fresnel and non-Frensel lenses, off-axis and dispersive lenses with binary stepped contours, and analog contours. Process details for all lens designs fabricated are given including multistep photolithography for binary fabrication and grayscale mask photolithography for analog fabrication. Reactive ion etching and ion beam milling are described for the binary fabrication process, while ion beam milling was used for the analog fabrication process. Examples of micro-optic components fabricated in both Si and CdTe substrates are given.

Anderson, W. W.↗
NASA NTRS1975

Empirical relation between interstellar X-ray absorption and optical extinction

An empirical relation between interstellar X-ray absorption and optical extinction is derived from the correlation of measurements made on objects of large intrinsic diameter. The result is Av = 4.5 times 10 to the -22nd power N(H) mag, with the principal error being largely systematic in origin, where N(H) represents the column density of interstellar matter in the Brown and Gould model for the X-ray absorption coefficient. Applying this ratio to optically identified compact sources, it is concluded that sources in binary systems showing pronounced X-ray occultations have an intrinsic absorption equivalent to about 10 to the 22-nd power atoms per sq cm of interstellar matter and that there are a few compact sources where the absorption seems to be primarily interstellar in origin. The interstellar absorption expected in Cyg X-1 from the extinction of its optical counterpart is much greater than that suggested by X-ray spectra, which may be due to a soft X-ray component greater than that predicted by the power law fitted to higher energy data.

Gorenstein, P.↗
NASA NTRS1992

Pulsar-irradiated stars in dense globular clusters

We discuss the properties of stars irradiated by millisecond pulsars in 'hard' binaries of dense globular clusters. Irradiation by a relativistic pulsar wind as in the case of the eclipsing millisecond pulsar PSR 1957+20 alter both the magnitude and color of the companion star. Some of the blue stragglers (BSs) recently discovered in dense globular clusters can be irradiated stars in binaries containing powerful millisecond pulsars. The discovery of pulsar-driven orbital modulations of BS brightness and color with periods of a few hours together with evidence for radio and/or gamma-ray emission from BS binaries would valuably contribute to the understanding of the evolution of collapsed stars in globular clusters. Pulsar-driven optical modulation of cluster stars might be the only observable effect of a new class of binary pulsars, i.e., hidden millisecond pulsars enshrouded in the evaporated material lifted off from the irradiated companion star.

Tavani, Marco↗
NASA NTRS1985

The 1984 eclipse of the symbiotic binary SY Muscae

Data from IUE spectra obtained with the 10 x 20-arcsec aperture on May 13, 1984, and optical spectrophotometry obtained with an SIT vidicon on the 1.5-m telescope at CTIO on April 29-May 1, 1984, are reported for the symbiotic binary SY Mus. The data are found to be consistent with a model of a red-giant secondary of 60 solar radii which completely eclipses the hot primary every 627 d but only partially eclipses the 75-solar-radius He(+) region surrounding the primary. The distance to SY Mus is estimated as 1.3 kpc. It is suggested that the large Balmer decrement in eclipse, with (H-alpha)/(H-beta) = 8.3 and (H-beta)/(H-gamma) = 1.5, is associated with an electron density of about 10 to the 10th/cu cm.

Kenyon, S. J.↗
NASA NTRS1973

Spectroscopic observations of HZ Herculis. II

Preliminary results from an extensive series of spectroscopic observations of the HZ Her optical counterpart of the eclipsing, pulsating X-ray binary Her X-1. Spectrograms with a dispersion of 30 A/mm reveal a spectral type as late as F5 near minimum in the light curve with the G-band and metallic lines present. Narrow Fe lines show that HZ Her is not a rapid rotator. Low-dispersion (115 A/mm) spectra, obtained with 10-minute time resolution, reveal rapid (10-min) variations in the 4640 N III emission and in the 4471 He I absorbtion features. The H-beta absorption is variable in equivalent width, and shows evidence of being partially filled with emission.

Bopp, B. W.↗
NASA NTRS1976

A model for the X-ray nova A0620-00

The model involves a white dwarf accreting mass from a late-type subgiant companion. The transient behavior of the X-ray source is explained by the instability to mass loss of the companion (as in Algol-type binaries). The brightening, spectrum, and decay timescale of the optical counterpart are explained in terms of re-emission of X-radiation intercepted by the subgiant. It was concluded that A0620-00 can provide an excellent test case for numerical models of stellar atmospheres irradiated by an external X-ray flux.

Endal, A. S.↗
NASA NTRS1976

A model for the X-ray nova A0620-00

A model is proposed for the transient X-ray source A0620-00 involving a white dwarf accreting mass from a late-type subgiant companion. The transient behavior of the X-ray source is explained by the instability to mass loss of the companion (as in Algol-type binaries). The brightening, spectrum, and decay timescale of the optical counterpart are explained in terms of re-emission of X-radiation intercepted by the subgiant. A0620-00 should provide an excellent test case for numerical models of stellar atmospheres irradiated by an external X-ray flux.

Endal, A. S.↗
NASA NTRS1981

SAS 3 observations of GX 1 + 4

GX 1 + 4 is one of the brightest celestial sources of high-energy X-rays. It is a pulsar with a period of approximately 2 min (perhaps a multiple of 2 min), decreasing at a variable rate which, since 1971, has averaged approximately 2% per year, but which can be larger than 5% per year. This is the largest rate of decrease observed for any pulsar. The rate of decrease appears to be correlated with the luminosity, in support of the idea that the period decrease is produced by accretion torques acting upon a neutron star. No evidence is seen for a Doppler shift due to motion of the pulsar in a binary orbit; this is consistent with the results of optical observations which suggest that any orbital period is fairly long (months to years). The spectrum of GX 1 + 4 is measured as a function of pulse phase, as well as the phase-averaged total spectrum, and the average spectrum of the pulses alone. The shape of the average pulsed spectrum suggests that the pulsations may be produced by 'hot spots' which are a few hundred meters in extent, with temperatures of approximately 10 to the 8th K (kT being approximately equal to 8 keV).

Doty, J. P.↗
NASA NTRS1981

Rapid X-ray and optical flares from Scorpius X-1

A 1 second time structure in X-ray flares from Sco X-1 and simultaneous optical flares with time structures no faster than 20 s are reported. The shortest reported time scale in the X-ray emission from Sco X-1 is decreased by a factor of 10, while remaining consistent with the parameters of the standard plasma model from Sco X-1. Different mechanisms for the production of X-ray flares and optical flares are suggested, and the production of optical flares by reprocessing on the surface of the binary companion of Sco X-1 is ruled out by the X-ray/optical flare time delay.

Petro, L. D.↗
NASA NTRS1994

Eclipse mapping of the accreting magnetic white dwarf in DP Leonis with HST

We present time-resolved ultraviolet spectrophotometry of the AM Her system DP Leo (E1114+182), obtained with the Faint Object Spectrograph on the Hubble Space Telescope (HST) in 1991 October. During this period, the binary was in a low-activity state. Complementary optical spectrophotometry and spectopolarimetry were obtained in 1991 October and December, as well as in 1992 April when the object had entered a high-accretion state. The HST spectrophotometry reveals two UV-emitting components-a hot 'spot' (T approximately 50,000 K, very approximately) near the magnetic pole into which most material is accreted, and the white dwarf photosphere (T approximately 16,000 K), which dominates when the spot is not in view. Both components appear as rapid and gradual components in the ingress and egress of secondary eclipse, the latter indicating a normal white dwarf radius of 0.8 x 10(exp 9) cm. The fractional area of the spot (f approximately 0.006) implied by the eclipse data is consistent with the observed UV flux and a minimum distance of 380 pc is similar to those found in other AM Her systems. The nearly identical eclipse light curves from the HST and earlier optical observations imply that the UV-emitting reprocessing area is not more extended than the cyclotron source of optical radiation in the accretion funnel. The timing of the onset of the bright phase indicated that the spot leads the secondary in orbital azimuth by approximately 3 deg.

Stockman, H. S.↗
NASA NTRS2003

An X-ray Investigation of the NGC 346 Field in the SMC (2): The Field Population

We present results from a Chandra observation of the NGC 346 cluster, which is the ionizing source of N66, the most luminous HII region and the largest star formation region in the SMC. In the first part of this investigation, we have analysed the X-ray properties of the cluster itself and the remarkable star HD 5980. But the field contains additional objects of interest. In total, 79 X-ray point sources were detected in the Chandra observation: this is more than five times the number of sources detected by previous X-ray surveys. We investigate here their characteristics in detail. The sources possess rather high hardness ratios, and their cumulative luminosity function is steeper than that for the rest of the SMC at higher .luminosities. Their absorption columns suggest that most of the sources belong to NGC346. Using new UBV RI imaging with the ESO 2.2m telescope, we also discovered possible counterparts for 36 of these X-ray sources and estimated a B spectral type for a large number of these counterparts. This tends to suggest that most of the X-ray sources in the field are in fact X-ray binaries. Finally, some objects show X-ray and/or optical variability, with a need for further monitoring.

Naze, Y.↗
NASA NTRS2007

Space Vehicle Pose Estimation via Optical Correlation and Nonlinear Estimation

A technique for 6-degree-of-freedom (6DOF) pose estimation of space vehicles is being developed. This technique draws upon recent developments in implementing optical correlation measurements in a nonlinear estimator, which relates the optical correlation measurements to the pose states (orientation and position). For the optical correlator, the use of both conjugate filters and binary, phase-only filters in the design of synthetic discriminant function (SDF) filters is explored. A static neural network is trained a priori and used as the nonlinear estimator. New commercial animation and image rendering software is exploited to design the SDF filters and to generate a large filter set with which to train the neural network. The technique is applied to pose estimation for rendezvous and docking of free-flying spacecraft and to terrestrial surface mobility systems for NASA's Vision for Space Exploration. Quantitative pose estimation performance will be reported. Advantages and disadvantages of the implementation of this technique are discussed.

Rakoczy, John↗
NASA NTRS2008

Space Vehicle Pose Estimation via Optical Correlation and Nonlinear Estimation

A technique for 6-degree-of-freedom (6DOF) pose estimation of space vehicles is being developed. This technique draws upon recent developments in implementing optical correlation measurements in a nonlinear estimator, which relates the optical correlation measurements to the pose states (orientation and position). For the optical correlator, the use of both conjugate filters and binary, phase-only filters in the design of synthetic discriminant function (SDF) filters is explored. A static neural network is trained a priori and used as the nonlinear estimator. New commercial animation and image rendering software is exploited to design the SDF filters and to generate a large filter set with which to train the neural network. The technique is applied to pose estimation for rendezvous and docking of free-flying spacecraft and to terrestrial surface mobility systems for NASA's Vision for Space Exploration. Quantitative pose estimation performance will be reported. Advantages and disadvantages of the implementation of this technique are discussed.

Rakoczy, John M.↗
NASA NTRS2011

Handbook of X-Ray Astronomy

X-ray astronomy was born in the aftermath of World War II as military rockets were repurposed to lift radiation detectors above the atmosphere for a few minutes at a time. These early flights detected and studied X-ray emission from the Solar corona. The first sources beyond the Solar System were detected during a rocket flight in 1962 by a team headed by Riccardo Giaccom at American Science and Engineering, a company founded by physicists from MIT. The rocket used Geiger counters with a system designed to reduce non-X-ray backgrounds and collimators limiting the region of sky seen by the counters. As the rocket spun, the field of view (FOV) happened to pass over what was later found to be the brightest non-Solar X-ray source; later designated See X-1. It also detected a uniform background glow which could not be resolved into individual sources. A follow-up campaign using X-ray detectors with better spatial resolution and optical telescopes identified See X-1 as an interacting binary with a compact (neutron star) primary. This success led to further suborbital rocket flights by a number of groups. More X-ray binaries were discovered, as well as X-ray emission from supernova remnants, the radio galaxies M87 and Cygnus-A, and the Coma cluster. Detectors were improved and Geiger counters were replaced by proportional counters, which provided information about energy spectra of the sources. A constant challenge was determining precise positions of sources as only collimators were available.

Arnaud, Keith A.↗
NASA NTRS1989

Auto- and hetero-associative memory using a 2-D optical logic gate

An optical associative memory system suitable for both auto- and hetero-associative recall is demonstrated. This system utilizes Hamming distance as the similarity measure between a binary input and a memory image with the aid of a two-dimensional optical EXCLUSIVE OR (XOR) gate and a parallel electronics comparator module. Based on the Hamming distance measurement, this optical associative memory performs a nearest neighbor search and the result is displayed in the output plane in real-time. This optical associative memory is fast and noniterative and produces no output spurious states as compared with that of the Hopfield neural network model.

Chao, Tien-Hsin↗
NASA NTRS1980

X-ray bursters and the X-ray sources of the galactic bulge

Type 1 X-ray bursts, optical, infrared, and radio properties of the galactic bulge sources, are discussed. It was proven that these burst sources are neutron stars in low mass, close binary stellar systems. Several burst sources are found in globular clusters with high central densities. Optical type 1 X-ray bursts were observed from three sources. Type 2 X-ray bursts, observed from the Rapid Burster, are due to an accretion instability which converts gravitational potential energy into heat and radiation, which makes them of a fundamentally different nature from Type 1 bursts.

Lewin, W. H. G.↗
NASA NTRS1993

Models of classical and recurrent novae

The behavior of novae may be divided roughly into two separate stages: quiescence and outburst. However, at closer inspection, both stages cannot be separated. It should be attempted to explain features in both stages with a similar model. Various simple models to explain the observed light and spectral observations during post optical maximum activity are conceivable. In instantaneous ejection models, all or nearly all material is ejected in a time that is short compared with the duration of post optical maximum activity. Instantaneous ejection type 1 models are those where the ejected material is in a fairly thin shell, the thickness of which remains small. In the instantaneous ejection type 2 model ('Hubble Flow'), a thick envelope is ejected instantaneously. This envelope remains thick as different parts have different velocities. Continued ejection models emphasize the importance of winds from the nova after optical maximum. Ejection is supposed to occur from one of the components of the central binary, and one can imagine a general swelling of one of the components, so that something resembling a normal, almost stationary, stellar photosphere is observed after optical maximum. The observed characteristics of recurrent novae in general are rather different from those of classical novae, thus, models for these stars need not be the same.

Friedjung, Michael↗